How can I combine w-4 and i-9 jotforms. I want a combination of PDFs of these two forms. Please guide me if I can do that

There is no direct option but you can use our Field Manager app to copy fields from one form to another: https://www.jotform.com/integrations/field-manager

After that when you create a PDF form you can see fields from both forms: https://www.jotform.com/help/212-how-to-create-a-pdf-form

Do try and let us know if this helps.